Isadore Harris, 72, a retired National Aeronautics and Space Administration scientist whose expertise was the study of the upper atmosphere, died of lung cancer Sept. 23 at Holy Cross Hospital. He lived in Silver Spring.

Dr. Harris was a theoretical physicist with the Goddard Space Flight Center for more than 35 years before retiring in 1992. He was among the first scientists to analyze data from U.S. Earth satellites in the late 1950s and calculated where Sputnik I would crash after its orbit.

An author of more than 90 scientific articles, he attended international conferences on orbiting research.

He was born in Syracuse, N.Y. He graduated from what is now Roosevelt University in Chicago, served in the Army during World War II and received a doctorate in theoretical physics from Northwestern University in Evanston, Ill.

He came to Washington in 1956 as a National Science Foundation Fellow at the Naval Research Laboratory.

In retirement, he volunteered as a homework helper at Long Branch Community Library in Silver Spring, tutoring students in math and science.

Survivors include his wife of 39 years, Ruth Roy Harris of Silver Spring; two sons, Jonathan Harris of Potomac and Geoffrey Harris of Chicago; a brother; and four grandchildren.